This invention relates to apparatus for tenderizing vaneer sheets.
The conventional apparatus for tenderizing veneer sheets may be divided into the following three main categories:
(a) apparatus including a pair of rotatable rolls covered, at their circumferences, with elastic material such as rubber which deforms when a veneer sheet is passed between the rolls, and between which the sheet is subjected to a tensile force so that small cracks are produced in the sheet;
(b) apparatus including a roll with a small radius of curvature against which a veneer sheet is pressed to be bent so that small cracks are produced therein; and
(c) apparatus including a number of cutters with which to cut a veneer sheet.
The foregoing apparatus (a) has the drawbacks that, since such an apparatus gives a tensile force to the sheet merely by producing friction between the sheet and the rolls, the portion of the sheet having a high mechanical strength may not be cracked, but the weak portion thereof may be excessively cracked, and that no cracks may be produced on the sheet if it is so orientated, when processed, that its fibers run at appreciable angles to the directions of the tensile force. Also, the foregoing apparatus (b) has the disadvantages that it can produce no cracks in veneer sheets with small thicknesses and that it cannot produce a sufficient number of cracks if the sheet is so orientated that its fibers run at appreciable angles to the direction of axis of the roll. With the foregoing apparatus (c), cuts or cracks may be made in the sheet irrespective of the fiber directions thereof, but it may cut the fibers crosswise and thus reduce the sheet strength, and it requires keeping the cutting tools sharp at all times.
Japanese Published Unexamined Utility Model Application No. 48-102274 discloses an apparatus for preventing a veneer sheet from being deformed to the shape of waves or eliminating such a deformation of the sheet. The apparatus includes a pair of rubber rolls each having, on their circumferences, a plurality of oblique grooves intersecting obliquely those of the other roll when the rolls contact each other. In this apparatus, the oblique projections on the rolls are pressed against the upper and lower surfaces of the sheet, and are elastically deformed, on these surfaces, in opposite directions, so that the sheet is subjected to a tensile force and is moderately deformed. This prior apparatus has the same disadvantage as the foregoing apparatus (a) in that the sheet may be cracked differently at its portions with different mechanical strengths. Also, this prior apparatus has the drawback that the tensile force it produces is not sufficient to produce cracks in a veneer sheet if the angle of the sheet fibers to the direction of the tensile force exceeds a certain limit.